1. Field of the Invention
The present invention relates to a 3-position 3-way solenoid valve for an anti-lock brake system, and more particularly to a 3-position 3-way solenoid valve for an anti-lock brake system having excellent assemblage and workability with a simple structure.
2. Description of the Prior Art
Currently, an anti-lock brake system which prevents locking of wheels during performing a braking operation of a vehicle to shorten a braking distance and improve steering is mounted to various vehicles. If wheels are locked during the braking operation to slide along a road surface, a frictional force between tires and the road surface is decreased to lengthen the braking distance and abruptly degrade a steering performance of a vehicle. The anti-lock brake system repeatedly increases, maintains or decreases a braking pressure exerting upon the wheels to impede the locking of wheels. It is generally referred to that the increase of the braking pressure is designated as a increase mode, maintaining thereof is a hold mode and decreasing thereof is a decrease mode. The anti-lock brake system is generally formed of a pressure generating source which is not a master cylinder, i.e., a pump and the like, valves operated by an electric signal, sensors for monitoring a rotating speed of the wheels and a controller for opening/closing the valves in accordance with a predetermined algorithm for attaining an effective braking operation.
FIG. 1 is a schematic circuit diagram of a hydraulic system showing a conventional anti-lock brake system utilizing two 2-position 2-way (hereinafter simply referred to as "2/2") solenoid valves of normally open and normally close types a increase mode, current is not supplied to first and second 2/2 solenoid valves S220 and S221 to open first valve S220 an outlet side of a hydraulic pump 110 and close second valve S221 at an inlet side of hydraulic pump 110, so that an oil pressure generated from hydraulic pump 110 is supplied to a brake wheel cylinder mounted to the wheel. In a static pressure mode, a current signal is supplied to first valve S220 to close first valve S220, thereby constantly maintaining the pressure of the brake wheel cylinder. In a decrease mode, the current signal is supplied to first and second valves S220 and S221 to close first valve S220 and open second valve S221, so that the pressure in the brake wheel cylinder is decreased. Such a system is stably operated, but two solenoid valves are employed with respect to a single channel to require eight solenoid valves in a 4-channel brake system. Therefore, the required number of valves are increased, and the overall brake system becomes bulky.
Meanwhile, in order to reduce the number of solenoid valves, an anti-lock brake system using a 3-position 3-way solenoid valve as shown in FIG. 4 has been developed to be currently available. When the 3-position 3-way solenoid valve is used, one solenoid valve is used per channel to reduce the required number of solenoid valves by half when compared with using the 2/2 solenoid valves.
FIG. 2 is a sectional view showing a conventional 3-position 3-way solenoid valve manufactured by BOSCH Co., in which an internal valve chamber is prevented from being contaminated by means of a filter 2 at the inlet and outlet thereof. A valve body 9 having a flow passage therein is placed immediately in front of an inlet valve 5 and immediately at the back of an outlet valve 4. The flow passage is opened/closed by inlet valve 5 and outlet valve 4. For the purpose of securing high reliability and minimum friction, an armature 6 is led by a non-magnetic bearing ring 3. A main spring 13 and an auxiliary spring 12 are installed in the center portion. A steel ball is soldered onto a carrier plate 11 to serve as a sealing member. A winding 7 is wrapped by a plastic to be protected from becoming wet by fluid. A first port 15 is communicated with a master cylinder 140 (refer to FIG. 5) and pump 120 (refer to FIG. 5), respectively. A second port 10 is communicated with a brake wheel cylinder mounted to a wheel, and a third port 1 is communicated with an accumulator 110 (refer to FIG. 5). A check valve 8 disposed in parallel with inlet valve 5 is opened when a brake is released to enable abrupt draining.
In the conventional 3-position 3-way solenoid valve as shown in FIG. 2, the flow passage is formed by penetrating the solenoid valve. If the solenoid valve is used to form a modulator, a modulator block is divided into upper and lower blocks to have respective flow passages connected to the respective ports of the solenoid valve. As the result, the structure of the modulator is complicated to deteriorate the assemblage as well as degrade workability.